The use of alkaline earth metal salts or organic carboxylic acids as additives for lubricating oil compositions is known. The said salts have a dispersant property so that they, when applied in such composition, ensure that the inside of engine cylinders remains clean and that deposition of carbonaceous products on pistons and in piston grooves is counteracted, so that piston-ring sticking is prevented.
It is also known to prepare basic (or overbased) alkaline earth metal salts of such acids. The overbasing provides an alkaline reserve which, when applied in lubricating oil compositions, reacts with and neutralises acidic compounds formed during the operation of the engine in which the composition is applied. Hence, sludge which may arise, it maintained dispersed due to the dispersant property of the salt while acids which would enhance sludge formation are neutralized. It is often desired for such basic salts to have a basicity index (BI), defined as the equivalents ratio of the total of alkaline earth metal to the total of organic acid, which is as high as possible. Examples of the salts are described in Great Britain Patent No. A-786167.
Another class of detergent additives are the so-called ashless dispersants. In U.S. Pat. No. 4,090,971 amides alkyl-substituted salicylic acids are described. The amines used to make the amides may be monoamines, including hydroxyamines, but are preferably polyamines, including diamines, for instance alkylene polyamines.
In U.S. Pat. No. 2,848,418 amides of salicylic acids are described, particularly formed from primary amines whose nitrogen atom is linked to secondary or tertiary carbon atom, i.e. comprising a branched alkyl group. The amide is said to improve the stability of lubricating oils.
In U.S. Pat. No. 3,110,670 lubricating oils containing the barium salts of primary N-alkyl amides of salicylic and other benzene hydroxy carboxylic acids are claimed to give improvements in oxidation stability of lubricating oils. The benzene ring may have methyl, hydrogen, sulpho or amino substituents. The compounds are oxidation inhibitors.
In U.S. Pat. No. 2,959,550 N-alkyl amides of aromatic para-hydroxy carboxylic acids are described as oxidation inhibitors for synthetic rubbers lubricating oils etc. The aromatic ring is usually unsubstituted but may be substituted by one or more alkyl groups, for instance containing 5 to 15 carbon atoms. The amides may be added in the form of the phenolate salts with alkali metals or alkaline earth metals.
A new compound according to the present invention is a multivalent metal ion salt of a compound of the formula XNR.sup.1 R.sup.2, in which R.sup.1 and R.sup.2 are the same or different and each are selected from hydrogen and hydrocarbon based radicals having from 1 to 30 carbon atoms, X is an acyl radical of an aromatic ortho-hydroxy carboxylic acid having a ring substituent which is a hydrocarbon based radical having at least 4 carbon atoms. The salt is oil-soluble.
Usually the multivalent metal ion is a divalent metal ion and is preferably an alkaline earth metal ion, for instance selected from Sr, Ba, Mg or Ca, usually Mg, preferably Ca.
Preferably at least one of R.sup.1 and R.sup.2 is a group other than hydrogen. Preferably one of R.sup.1 and R.sup.2 is hydrogen. A hydrocarbon based radical represented by R.sup.1 and/or R.sup.2 is attached via a carbon atom to the amide nitrogen atom and may be aliphatic, alicylic, aromatic, alkaryl, aralkyl. In one class of preferred compounds the alkyl radical is a lower alkyl radical, for instance having 1 to 6 carbon atoms. Another class of compounds has a long chain alkyl group for instance having 4 to 24 carbon atoms. Any alkyl chains may be branched or straight chain. It may for instance be a radical in which the carbon atom attached to the nitrogen atom is a secondary or tertiary carbon atom. The radical may contain non-hydrocarbon substituents which do not alter the predominantly hydrocarbon character of the radical such as halogen atoms, nitro groups, cyano groups, ether groups, ester groups, amide groups, ketone groups, sulphone groups and sulphoxide groups, as well as chains with hetero atoms, such as oxygen, sulphur, or nitrogen atoms.
The aromatic radical may comprise a napthalene ring or, preferably, a benzene ring. Where the ring is a naphthalene ring, the compound may have the hydroxyl and carbonyl groups attached to the ring at any available positions, as long as they are ortho to each other. The aromatic ring may comprise substituents other than the hydrocarbon substituent, which do not interfere the activity of the compound as an oxidation inhibitor or with the process for producing the compound. For instance it may comprise other hydrocarbon substituents, such as lower alkyl substituents, as well as halogen atoms, sulpho groups and amino groups. Usually there are no additional substituents.
The hydrocarbon-based ring substituent is a radical having a carbon atom directly attached to the ring and has a predominantly hydrocarbon character, i.e., promotes oil solubility. It is usually in the position ortho or gas to the hydroxyl group but meta is also possible. Examples of of such radicals are hydrocarbon radical such as aliphatic, alicyclic, aromatic, alkaryl or aralkyl usually a C8 to 30, preferably C10 to 24-alkyl group, which may branched or straight chain; substituted hydrocarbon radicals, i.e. radicals containing non-hydrocarbon substituents which do not alter the predominantly hydrocarbon, hydrophobic character of the radical, such as halogen atoms, nitro groups, cyano groups, ether groups, ester groups, amide groups, ketone groups, sulphone groups and sulphoxide groups, as well as chains with hetero atoms, such as oxygen, sulphur, or nitrogen atoms.
It is most convenient for the group X to comprise the acyl radical of a C.sub.6 to 30 alkyl salicyclic acid.
The product of the invention is preferably "overbased", that is it comprises a greater than stoichiometric amount of metal than required to neutralise the phenolate ion. Overbased products can be described in terms of their "basicity index" (BI), which is defined as the ratio of total equivalents metal to equivalents of the acyl groups (or amide groups) in the X group of the compound. An overbased product generally has excess of metal (hydr)oxide and may also comprise the carbonate of the metal. An amide overbased with lime and which is subsequently carbonated may for instance be represented by the following formula: ##STR1##
There is also provided in the invention a process for producing the new compounds, in which a compound of the formula XY is reacted with an amine of the formula HNR.sup.1 R.sup.2, in which Y is OR.sup.3, in which R.sup.3 is hydrogen, alkyl, aryl or acyl, or Y is a halogen atom, and R.sup.1 and R.sup.2 are as defined above, followed by the reaction of the amide with a multivalent metal compound to produce the salt.
Usually the metal compound with which the amide is reacted includes the metal oxide or hydroxide. Preferably the metal compound is added in greater than stoichiometric, or equivalent, amounts, to give an overbased product. Usually the reaction to produce the salt is followed by a carbonation reaction for instance carried out as described in Great Britain Patent No. 8613815, Great Britain Patent No. 8627130 or Great Britain Patent No. 871159.
The amidation of the present invention uses the ring-substituted acid or derivative as its starting material. In general these are readily available and it has been found that it is easier to carry out that amidation than a process in which the amide of an unsubstituted aromatic acid is subsequently reacted to introduce the required substituent into the ring.
Although the process may be carried out using the acid as the starting material, it is generally found to be preferred for the process to use a derivative of the acid as its starting material, for instance the acid chloride or acid anhydride or most conveniently the ester. Usually the ester is formed from the acid by reaction with a C1 to 6 alkanol by conventional esterification techniques. It is convenient for the alcohol to have at least 3 atoms, for instance 4 atoms, since the esterification reaction can then be driven by removal of water and a higher reaction temperature can be used.
The amidation process starting from the ester is usually carried out with an excess of the amine. Excess amine and the alcohol which is produced are removed from the product by distillation.
In the amidation reaction using the acid chloride as the starting material it is important to remove the hydrogen chloride which is formed as a by-product. In general this is done by washing with water, in the normal way. This route is less preferred than starting with the ester because of the difficulty of ensuring complete removal of chloride or other halide.
In an alternative process for producing the new products, the acid X-OH may be reacted with urea, or a thiourea or substituted ureas. Reaction with urea produces the amide which can, if desired, be subsequently alkylated by known techniques.
The reaction to produce the salt is carried out by conventional techniques, for instance by reaction with a metal compound, usually a (hydr)oxide, in organic solution, for instance in a solvent comprising xylene and methanol. As stated above the product is preferably an overbased product, that is formed by a reaction in which there is a stoichiometric excess of metal compound added. Such an overbasing reaction may for instance be carried out as described in Great Britain A-786167. Usually the overbasing reaction additionally comprises a carbonation step, in which the product of the reaction between an excess of metal compound and amide in a solvent solution is contacted with carbon dioxide at a slightly raised temperature. Such processes are for instance as described in Great Britain Patent No. 8613815, Great Britain Patent No. 8627130 and Great Britain Patent No. 8716159.
The product may optionally be borated as described in Great Britain Patent No. 8330441.
The invention provides also for the use of new compounds as additives in lubricating oils, greases or other oil-based systems. For instance, the compounds have oxidation inhibiting properties and may be used in any of the applications where an oil-soluble oxidation inhibitor is required, for instance in polymer composition, including rubbers, and in various viscous organic liquids, such as oils and greases. The compounds also have detergent and dispersant properties in lubricating systems and their use in those compositions can additionally give improved friction properties as well as oxidation stability.
The compounds of the present invention are found to have properties which are similar to the overbased salicyclic acid compounds described in the above mentioned publication. The compounds are thought to form micelles in oil solution, in which the inorganic base particles (Ca(OH).sub.2, CaCO.sub.3, MgO, etc) can be incorporated to generate a colloidal, for instance overbased, but oil-soluble detergent. The alkaline reserve of the overbased products allows neutralisation of acidic compounds formed during the operation of an engine which is lubricated by a composition containing the compounds.
Lubricating oil compositions in the invention comprise a major amount of a lubricating base oil and minor amount of the salt as described hereinbefore.
The lubricating base oil will conveniently constitute more than 50% w, preferably more than 80% w, of the composition. It can be selected from mineral lubricating oils of varying viscosities, but it also includes a synthetic lubricant, such as ester-type lubricant or a polyolefin-type fluid, or a vegetable oil, or a grease.
Fuel compositions which are used in marine diesel engines usually contain some sulphur compounds. To neutralize the acidic compounds formed from these sulphur compounds a relatively high concentration of the basic salt is employed. Preferably, these marine lubricating oil compositions contain from 5 to 30% w of the salt. Lubricating oil compositions for road engines may contain lower concentrations. The amount of salt in these lubricating oil compositions is preferably from 0.01 to 5% w, in particular from 0.1 to 4.0% w.
Fuels, such as gasolines, kerosine, diesel fuel and gas oils, can also contain the above salts. The amount of these salts is similar to that in road engine lubricating oil compositions or lower; conveniently the amount is from 0.001 to 5% w, in particular from 0.01 to 1.0% w.
The lubricating oil composition can be prepared by mixing a concentrate containing a major portion of salt, i.e., containing up to 60% w of a salt as described above, in a lubricating oil, with a lubricating base oil to give the desired concentration. The composition should contain a major portion of base oil, i.e., greater than 50% w, and a minor portion of salt, i.e., less than 50% w. Such a concentrate is conveniently prepared by addition of a lubricating oil to the product obtained after completion of step c), and removal of any volatile hydrocarbon solvent, water and alcohol, if present. The lubricating oil may be the same as the one indicated above as a suitable hydrocarbon solvent. The concentrate may conveniently contain a stabiliser, which is selected from a variety of organic compounds, such as those described in British patent specification No. 818,315. These compounds include mono- or polyhydric alcohols, alkyl amines and alkyl phenols.
The lubricating oil compositions may further contain a number of other additives, such as antioxidants, foam inhibitors, corrosion inhibitors, viscosity index improvers, and pour point depressants, as can be established by a person skilled in the art. The compounds can be used in combination with other dispersants and detergents.
The ranges and limitations provided in the instant specification and claims are those which are believed to particularly point out and distinctly claim the instant invention. It is, however, understood that other ranges and limitations that perform substantially the same function in substantially the same way to obtain substantially the same result are intended to be within the scope of the instant invention as defined by the instant specification and claims.